Thermal processing oven in a blow-forming facility for thermoplastic receptacles

ABSTRACT

An oven in a production facility for thermoplastic receptacles, including a conveyor chain which is provided with gripping devices ( 16 ), whereby each gripping device engages axially with the neck of a receptacle blank in order to transport it into the oven. The gripping devices are displaced axially by a mechanism which is provided with an arm ( 44 ) which can move along a path that is substantially parallel to the axial direction (A n ) in which gripping takes place and which bears an interface element ( 40 ) which is designed to come into contact with the gripping device ( 30 ). The interface element ( 40 ) is movably mounted on the arm ( 44 ) to enable slip-free contact with the gripping device while it is immobilized in relation to the arm according to the axial direction in which gripping occurs.

BACKGROUND OF THE INVENTION

The invention concerns processes for manufacturing hollow bodies fromthermoplastic material in which a preform is first produced by injectionbefore obtaining the final container in the course of a process thatincludes at least one blow-molding step.

The preform obtained by injection generally has a tubular, cylindricalbody closed at one of its axial ends and which at its other end isextended by a neck, also tubular. The neck is generally injected so asto already have its final form when the body of the preform is requiredto undergo relatively substantial deformation to form the finalcontainer following the blow-molding operation.

More particularly, these processes concern the manufacture of containersmade of polyethylene terephtalate (PET).

There are several variations of the procedures in this family. Dependingon the process used, the corresponding manufacturing facility has one ormore temperature condition ovens.

In all of the processes concerned, the blow-molding operation of thebody of the preform requires that said preform be brought to atemperature that is higher than the glass transition temperature of thematerial. To that end, the preform is temperature conditioned bycirculating it inside an oven. The oven has heating means which are, forexample, comprised of infrared lamps in front of which the preform ismoved by a conveyor device. Advantageously, provision is made so thatthe preform rotates while it is moving through the oven.

The preforms are generally held on the conveyor device by a grippingdevice formed by a mandrel that is engaged inside the neck of thepreform and which holds it by tightening against the inner face of theneck. However, in some cases the preform is held by the outer face ofthe neck.

In some of these processes, the temperature resistance of the body ofthe final container is increased by increasing the rate of crystallinityof the PET. This is achieved by first putting the preform through afirst blow-molding stage to obtain an intermediate container that issubjected to a heating stage in a temperature condition oven, duringwhich stage it shrinks. This shrunk container undergoes a secondblow-molding stage which gives the container its final form.

In other processes, it is the neck of the preform, of the finalcontainer or of an intermediate container, that is heated to increasethe crystallinity. To that end, the facility has a suitable temperaturecondition oven.

In all of these cases, it can be seen that facilities that manufacturecontainers from thermoplastic material can have several types oftemperature condition ovens, which ovens, of course, are suitable forthe heat treatment to be carried out. However, all of these ovens mayhave the same type of conveyor system.

These different ovens, therefore, are intended to process objects indifferent phases of producing the final container. However, they are allintended to grip this object by the neck, which does not undergo anyfundamental variation in its geometry, even if some processes result ina modification of the structure of the material of which the neck iscomposed. Also, in the text that follows the terms preform, blank orbottle are used indiscriminately to designate the object to be processedin the oven.

According to a known technique, the conveyor system can, for example, becomprised of a chain of conveyor links intended to carry a preform or ablank of the container in order to move it around a circuit inside theoven. This chain is driven in continuous movement.

To pick up the preform, a conveyor link has a gripping device that isaxially movable with respect to the link and which, when it is takenfrom an extreme release position to an extreme gripping position, isaxially engaged on the neck of the blank.

Different means are known for controlling the movements of the grippingdevices between their released and gripping positions. Thus, in generala system of cams and cam followers is used to take advantage of the factthat, in general, the movement of the gripping devices is perpendicularto that of the conveyor chain. In a conventional manner, each grippingdevice is equipped with a roller which is intended to cooperate withsloping ramps that are integral with the infrastructure of the oven tocause the gripping device to raise or lower to the level of the preformloading or unloading stations.

However, in some cases the means for controlling the cams is notentirely satisfactory. This is especially the case when the grippingdevice has a mandrel that is intended to be inserted and very tightlysecured inside the neck of the preform.

The loading and unloading of the preform, then, requires a relativelysizeable force applied along the axis of the gripping device. With asystem of cams, such axial force becomes even greater, exerted on theconveyor chain in the direction of movement of said conveyor. Thus, eachtime a roller comes into contact with a cam, the chain jerks. This isharmful, first to the proper synchronization between the chain and theother components of the blow-molding facility, and second, to theworking life of the conveyor system. This jerk becomes greater as thespeed of movement of the gripping device increase, because then a camwith a steep slope will have to be used. In addition, in this case, thecontact pressure between the roller and the cam becomes heavy to thepoint of threatening the working life of these two elements.

Moreover, in known embodiments, the roller is offset with respect to theaxis of movement of the gripping device. Also, when the loading orunloading effort is large, the roller causes a sizeable rotationaltorque on the corresponding link of the chain, which can be the sourceof premature wear of the conveyor system.

A purpose of the invention, therefore, is to propose new means ofcontrolling the movements of the gripping devices that make it possibleto limit the forces on the conveyor chain even when the force in loadingand unloading the preform is large.

SUMMARY OF THE INVENTION

To that end, the invention proposes a temperature condition oven for ablow-molding facility for producing containers of thermoplasticmaterial, of the type with a conveyor chain of links having grippingdevices each of which is intended to carry a blank of the container inorder to move it around a circuit inside the oven, of the type in whichthe chain is driven in continuous movement along its circuit, of thetype in which each gripping device is axially movable with respect tothe link that carries it so that when it is taken from an extremerelease position to an extreme gripping position it engages axially onthe neck of the blank, and of the type in which it is provided withmeans to control the movements of the gripping devices between theirrelease and gripping positions, characterized in that the means forcontrolling the movements of the gripping devices comprise at least onemechanism provided with an arm that is movable along a trajectory thatis essentially parallel to the axial direction of gripping and whichcarries an interface device intended to come into contact with thegripping device, and in that the interface device is movably mounted onthe arm in such a way as to allow non-slip contact with the grippingdevice while being immobilized with respect to the arm along the axialdirection of gripping.

According to other characteristics of the invention:

the arm is controlled in its trajectory along a movement that alternatesbetween an initial position and a final position; and, for a position ofcontact of the arm that falls between its initial and final positions,the interface device comes into contact with the gripping device whichis in one of its extreme positions and forces it towards the other ofits extreme positions, which position corresponds to the final positionof the arm;

the interface device is mounted on the arm so that it is movable in adirection parallel to the movement of the links of the chain;

the interface device is elastically drawn back to a rest position withrespect to the arm, and as a result of the movement of the correspondingchain link between the moment the arm comes into contact with theinterface device and the moment the arm reaches its final position, theinterface device is moved away from its rest position by the grippingdevice with which it is in contact;

between the contact position and the final position of the arm, thegripping device cooperates by adherence to the interface device to moveit away from its rest position with respect to the arm;

during the return movement of the arm from its final position to itsinitial position, the interface device is drawn back to its restposition by elastic means;

the interface device is mounted on the arm slideably in the direction ofmovement of the links of the chain;

the interface device is comprised of at least one roller which ismounted on the arm rotatably around an axis perpendicular to the axialdirection of gripping and to the direction of the movement of the linksof the chain;

between the moment the interface device comes into contact with thegripping device and the moment the arm reaches its final position, thegripping device cooperates by adherence to the interface device to drivethe roller in rotation around its axis;

the gripping device has a rod one central section of which is axiallyguided in the corresponding link and the two opposite ends of whichcooperate respectively with the blank and with the mechanism, themechanism exerting a pushing force on the rod, and the interface devicecooperates by pressing against one surface of the rod that isessentially flat and perpendicular to the axial direction;

the gripping device has a rod one central section of which is axiallyguided in the corresponding link and the two opposite ends of whichcooperate respectively with the device and with the mechanism, themechanism exerts a pulling force on the rod, the interface device hasthe shape of a U-section having two parallel limbs, the ends of whichare turned inward to delimit an aperture allowing the rod to passthrough, the rod of the gripping devices has a control head which isintended to move between the two limbs of the U-section and which has awidth that is greater than the width of the aperture in such a way thatwhen the interface device is moved axially by the arm, the turned endsof the U-section cooperate with the head to control the axial movementof the gripping device;

the gripping device has a rod one central section of which is axiallyguided in the corresponding link and the two opposite ends of whichcooperate respectively with the blank and with the mechanism, themechanism exerts a pulling force on the rod; the arm has the shape of aU-section having two parallel limbs, the ends of which are turned inwardto delimit an aperture allowing the passage of the rod; each of the twoturned ends has at least a roller; the rod of the gripping devicescarries a control head that is intended to move between the two limbs ofthe U-section and which has a width that is greater than the width ofthe aperture in such a way that when the arm is moved axially, therollers of the turned ends of the U-section cooperate with the head tocontrol the axial movement of the gripping device;

the alternating movement of the arm is controlled by a connecting rodand crank system; and

the means for controlling the movements of the gripping means comprisetwo mechanisms, one of which controls the movement of the grippingdevices from their extreme release position to their extreme gripposition, and the other controls the reverse movement.

BRIEF DESCRIPTION OF THE DRAWINGS

Other characteristics and advantages of the invention will appear fromthe detailed description that follows, as well as in the appendeddrawings in which:

FIGS. 1 and 2 are axial cross sectional views that illustrate thegripping device of one link of the conveyor chain, this device beingillustrated respectively in one high released position and in one lowposition gripping a preform;

FIG. 3 is a perspective view illustrating one embodiment of a mechanismto control the movements of the gripping device;

FIG. 4 is a cross sectional view of the control means illustrated inFIG. 3, providing additional illustration of the versatile tool on thismechanism to control the movement of the gripping device from its upperto its lower position, this tool being more particularly illustrated inperspective in FIG. 5;

FIG. 6 illustrates, in perspective, a versatile tool on the controlmechanism to return the gripping device from its lower to its upperposition;

FIGS. 7A to 7D illustrate, diagrammatically in axial cross section, anoperation allowing the gripping of the preform;

FIGS. 8A to 8D illustrate in the same way an operation allowing therelease of the preform; and

FIGS. 9 and 10 are views similar to those of FIG. 3 illustratingvariations of embodiment of the invention.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

The invention will now be described in the particular case of atemperature condition oven for a preform 10 made of thermoplasticmaterial, for example PET. The preform 10 is produced by injectionmolding and it has a neck 12 which is formed directly in its final form,the neck having an external radial flange 14. For reasons of clarity ofthe description, in all of the text hereinafter the preform 10 will beconsidered to be arranged vertically, neck upward, as illustrated forexample in FIGS. 1 and 2. The geometric terms used to describe theinvention are the result of this convention and should not be consideredto be limitations to the scope of the invention.

FIGS. 1 and 2 illustrate partially and diagrammatically the grippingdevice 16 of a conveyor link the principal body 18 of which is onlyillustrated very partially. The principal body 18 is intended to beconnected to two other similar links by being articulated with respectto them around a vertical axis to form a part of a conveyor chain forpreforms in the oven. In this example, the chain moves essentially in ahorizontal plane. However, the conveyor links and their linkages can bedone differently without going beyond the scope of the invention. Theycan even be independent of each other, provided, however, that they havesynchronized drive means so that two links are separated at the samerate, at least in the area where the preform is gripped.

The gripping device 16 has a cylindrical rod 20 with a vertical axisA_(n) which is rotatably mounted around its axis in a sleeve 22 whichitself is slidably mounted in the main body 18 along the axis A_(n). Therod 20 and the sleeve 22 are axially integrated with each other in sucha way that the gripping device 16 can slide between two extremepositions, that is, an upper released position, illustrated in FIG. 1,and a lower gripping position illustrated in FIG. 2.

The sleeve 22, which is generally cylindrical in shape, has two lateralflats 24 that extend axially along the length of travel of the grippingdevice and which are diametrically opposed. The link has friction pads26 that are radially applied in support by springs 28 against the flats24 in order to maintain by braking the axial position of the sleeve 22,and thus the gripping device 16.

At its upper end, the rod 20 has a control head 30 that is generallycylindrical in shape. At its base, the head 30 has a gear wheel 32 thediameter of which is greater than that of the sleeve 22 in order tocooperate with a fixed rack (not represented) of the oven in order tocause the rotation of the rod 20 around its axis A_(n) when the conveyorlink moves in the oven.

At its lower end, the rod 20 has a gripping mandrel 34 which has a shapesuitable for the neck 12 of the preform 10. The mandrel 34 representedhere has an essentially cylindrical shape, but in practice its shape canbe more complex. Of course, should it be desired to pick up the preformby the outside of the neck, the mandrel 34 would be replaced for exampleby a bell-shaped gripper.

In order to perform the gripping of the preform 10 at the entrance tothe oven, the mandrel 34 should be axially engaged downward inside theneck 12 of the preform 10, which is achieved by moving a gripping device16 assembly from its upper position to its lower position.

The mandrel is received and tightened in the neck, which means that theengagement requires a certain force along the direction of the axisA_(n). This force is primarily dependent on the degree of tightening,and as an example it can reach about 150 daN in certain applications. Itwill be noted that the recovery from the axial gripping force by thepreform is done, for example, by support of its flange 14 on a supportsurface 4 as part of the conveyor link.

Once engaged in the neck 12, the mandrel 34 can then carry the preform10 and can also rotate it around its axis A_(n).

Upon exiting the oven, the mandrel 34 must be axially disengaged upwardto release the preform 10. Since the mandrel tends to carry the preform10 upward with it, ejection means must be provided that prevents it frommoving upward. To that end, the conveyor link has a tubular ejector 36with axis A_(n) which is integral with the main body 18 of the link andthe inside diameter of which is essentially equal to the inside diameterof the neck 12 of the preform 10.

In the released position, the mandrel 34 is received inside the ejector36, while in the lower position, the mandrel 34 passes below the lowerend of the ejector 36. This ejector is arranged in such a way that itslower edge is situated just above the upper edge of the neck of thepreform 10.

Also, when the preform 10 is lifted up by the mandrel 34, it is blockedagainst the ejector 36. The mandrel 34 continues upward and ends bycompletely disengaging from the neck 12 of the preform, and the preformis thus released. Of course, the ejector could also be supported againstthe flange 14.

More particularly, the invention concerns the means that make itpossible to control the gripping device 16 between its upper and lowerpositions.

More precisely, the oven according to the invention has means at theentrance of the oven that make it possible to control the grippingdevice 16 from its upper position to its lower position in order tocontrol the gripping of the preform, and upon exiting from the oven,means that allow it to return from its lower position to its upperposition. These two means are very similar and have two identicalmechanisms 38 on which a specific tool is adapted for controlling theraising or lowering.

The common mechanism 38 is illustrated in perspective in FIG. 3 and incross section in FIG. 4. In FIG. 4, also illustrated is a push tool 40specific to controlling the descent in order to ensure the gripping ofthe preform 10.

The mechanism 38 has a frame 42 which is intended to be attached to thebody of the oven. On this frame 42, a bracket shaped arm 44 is mountedso as to be able to slide along the gripping direction, that is, in thisinstance in the vertical direction. To do this, a sliding connection isused formed by a vertical rail 46 integral with a vertical upright 50 ofthe bracket 44, and by a slide 48 attached to the frame 42.

The mechanism has means to cause an alternating movement of the bracket44 along the axial direction of gripping. In the proposed example, asystem of a connecting rod 84 and crank 86 is used, driven by a rotaryelectric motor 88 in the horizontal axis. Of course, any other knownmeans to produce an alternating axial movement of the bracket 44 can beused. Thus, the movements of the bracket could be controlled by anactuator.

At the lower end of its vertical upright 50, the bracket-shaped arm 44has a horizontal lower plate 52 on the lower face of which is attached ahorizontal rail 54 comprising part of a second sliding connection. Amovable slide 56 is mounted on the horizontal rail 54 so as to be ableto slide with respect to the bracket 44 along a horizontal directionwhich is therefore perpendicular to the vertical direction of grippingof the preform and which corresponds to the direction of movement of thepreform conveyor chain.

The movable slide 56 is intended to carry one or the other of the twospecific tools 40, 60, illustrated in more detail in FIGS. 5 and 6,respectively.

Each of these two tools 40, 60 comprises an upper plate 62 which isprovided with indexing orifices 64 intended to receive indexing studs 58extending axially downward from the movable slide 56. The plate 62 isattached to the slide 56, for example, by two screws (not shown).

Each of the two tools 40, 60 also has a support plate 66 which extendsin a vertical plane perpendicular to the sliding direction of themovable slide 56 and which is intended to be attached directly to thelower plate 52 of the bracket 44, the support plate 66 of each tool tocarries two parallel guides 68 which extend in the sliding direction ofthe movable slide 56 and each of which is slidably received through aguide hole made in the plate 62. The guides 68 serve to supporthelicoidal compression springs 70 which are placed between the plate 62and the support plate 66 to separate them. The free end of the guides 68has a bulge against which the plate 62 is pressed by the action of thesprings 70.

Thus, when one or the other of the two tools 40, 60 is mounted on themovable slide 56, the plate 62 can slide along the horizontal directionwith respect to the bracket 44. However, under the action of the springs70, it is returned to a rest position in which it is stopped against thebulges 72 of the guides 68.

Illustrated in FIGS. 4 and 5 is the push tool 40 intended to control thedownward movement of a gripping device 16 simply by supporting on theupper face the control head 30 of said gripping device. The push tool 40has a tubular stem 74 which extends axially downward from the plate 62and which has fine pitch threads on its internal face to allow theattachment and precise axial positioning of a cylindrical stud 76 thelower face of which is intended to contact the control head 30 to causeit to descend. A lock nut 78 allows the stud 76 to be secured on thestem 74 to prevent any maladjustment of its axial position.

The fork tool 60 illustrated in FIG. 6 has two legs 80 in the form ofparallel plates that extend vertically downward from the plate 62. Eachleg 80 has, at its lower end, a transversal internal flange 82 thatextends toward the other leg. The transverse separation and the heightof the legs 80 are greater than the corresponding dimensions of thecontrol head 30 so that said head can move between the two legs.However, the transverse separation of the two flanges is greater thanthe diameter of the sleeve 22 but less than that of the gear wheel 32 sothat, when the head 30 is received between the two legs 80 and the forktool 60 is moved upward, the flanges 82 cooperate with the lower face 33of the head 30 to draw it upward.

The diagrams in FIGS. 7A to 7D illustrate the operation of the controlmeans according to the invention in the case of gripping the preform. Inthese diagrams, the control head 30 of two successive links of theconveyor chain is represented. The axes of the gripping devices of thesetwo links are, respectively, A_(n) and A_(n+1).

At the stage illustrated in FIG. 7A, the bracket 44 is in an initialupper position and it can be seen that the control head 30 of one of thelinks is approaching in the direction of movement of the conveyor chain,that is, from left to right in the figures. The lower face of the stud76 of the push tool is then situated higher than the control head 30.

At that moment, the connecting rod and crank system causes the bracketshaped arm 44 to begin to descend. The push tool 40 is then in the restposition with respect to the bracket, that is, held to the left by thesprings 70.

At stage 7B, the link of the conveyor chain is seen to have moved inline with the push tool 40. This moment corresponds essentially with themoment at which the lower face of the push tool 40 comes in contact withthe control head 30. In reality, it can be seen that the push tool 40and the control head 30, although they are essentially of the samediameter, only cooperate by half of their respective surfaces becausecontact occurs before their axes A_(n) and X-X coincide. It will benoted that the push tool 40 is still in the rest position with respectto the bracket 44.

At this moment, with the downward movement of the bracket 44 continuing,the push tool exerts a downward pressure on the control head, whichallows the gripper mandrel 34 to penetrate inside the neck 12 of thepreform. However, all during the downward movement of the push tool 40and of the control head 30, the latter continues to move with the linkof the conveyor chain in the horizontal direction, while the bracket 44can not move in that direction. Also, as can be seen in FIG. 7C, thepush tool 40 is then horizontally separated from its rest position bythe head 30 by the sliding of the movable slide 56 with respect to thebracket 44 by compressing the springs 70.

In the proposed example, this actuation of the push tool 40 is theresult of simple adherence of the lower face of the push tool 40 on thehead 30, with no slippage on one with respect to the other, thisadherence being the result of the axial gripping effort necessary toallow the engagement of the mandrel 34 in the neck of the preform.

When the bracket 44 has reached its final lower position, the connectingrod and crank system then begins the movement back upwards. The contactbetween the push tool 40 and the control head 30 is then broken so thatthe latter, braked by the pads 26, has reached its extreme lowerposition of gripping the preform. It will be noted, then, that theextreme lower position of the gripping device 16 is determined by thefinal lower position of the push tool 40. Having a push tool in twoparts, in which the position of the cylindrical stud 76 can be adjustedwith respect to the plate 62, makes it possible to define precisely theextreme lower position of the gripping device 16, as well as to defineprecisely the distance at which the mandrel 34 is engaged in the neck ofthe preform.

Moreover, as can be seen in FIG. 7D, as soon as contact with the controlhead is broken, the springs 70 force the push tool 40 back to its restposition with respect to the bracket 44. Thus the mechanism returns toits initial configuration. In addition, it can be seen that the controlhead 30 of the next link then arrives in position to be, in its turn,moved downward by the push tool 40.

In a similar way, FIGS. 8A to 8D illustrate the operation of the controlmeans at the moment the preform is released.

In FIG. 8A, the mechanism is illustrated in its initial lower position,before the control head 30 of the first of the two links arrives at thefork tool 60. It will be noted that the flanges 82 of the legs are thensituated below the lower face 33 of the head 30 which is in its extremelower position. In this way, the head 30 can then be engaged between thelegs 80 as a result of the movement of the conveyor chain.

Illustrated in FIG. 8B is the contact position of the bracket 44 forwhich the flanges 82 come into contact with the head 30 during theirupward movement. Here again the contact occurs before the head isexactly in line with the fork tool 60.

In FIG. 8C, the bracket 44 has reached its final upper position, causingthe head 30 to move to its extreme upper position. At the same time,because of the effort required to extract the mandrel 34, the head 30causes the fork tool 60 to move horizontally with respect to the bracket44 by compressing the springs 70.

At that moment, the connecting rod and crank system causes the bracket44 to descend again and thus break contact with the flanges 82 of thehead 30, which remains in the upper position due to the pads 26.However, the springs 70 then return the fork tool 60 to its restposition. In spite of this, the fork tool can return to its initiallower position before the next control head, with axis A_(n+1), comesinto position of contact.

In the proposed example, the electric motor 88 turns at a constant speedso that the raising and lowering times of the tools 40, 60 areidentical. However, it could be provided that the motor be controlled sothat one of the two movements, up or down, is faster than the other, forexample in order to avoid any risk of interference of the tool with thenext head during the return movement. This possibility could also beused to obtain a predetermined speed of movement of the gripping device,independent of the speed of movement of the conveyor chain, which islinked, for example, to the production rate of the blow-molding machineassociated with the oven.

FIGS. 9 and 10 illustrate two mechanisms according to the principles ofthe invention but in which the interface devices by which the mechanismacts on the head 30 of the rod 20 are not slidably mounted on the arm44, but are comprised of at least one roller rotatably mounted on thearm 44 around a horizontal axis so as to be able to roll on the head 30of the rod 20.

In FIG. 9, it can be seen that under the lower plate 52 of the arm 44, atool has been mounted to control the gripping device 16 from its upperposition to its lower position. This tool comprises a single roller 98rotatably mounted in a fork joint 96 around a horizontal axis Y-Y whichin turn is perpendicular to the axial direction of gripping and to thedirection of movement of the conveyor chain. The fork joint 96 isrigidly attached beneath the lower plate 52.

In this way, when the arm 44 is moved from its upper position to itslower position, the roller 98 comes into contact against the controlhead 30. Once in contact, the roller 98 can push the rod 20 downward. Atthe same time, because of the movement of the link 18, the roller 98rolls on the head 30 without inducing any parasitic force on the link.

In FIG. 10, a tool 91 is represented that is intended to be attacheddirectly beneath the lower plate 52 of the arm 44 to provide the raisingof the gripping device to its upper position. This tool 91 has a shapesimilar to that of the fork tool 60 described above, and it thereforehas two parallel legs 90, each of which has at its lower end an internaltransverse flange 92.

However, in this embodiment of the invention, the tool 91 is fixed withrespect to the arm 44 but the flanges 92 of the legs 90 are each fittedwith two rollers 94 which are mounted rotatably around their axes, whichin turn are perpendicular to the axial direction of gripping and to thedirection of movement of the conveyor chain. These rollers 94, whichextend above the upper face of the flanges 92, are intended to come incontact with the lower face 33 of the head 30.

Thus, when the arm 44 causes a gripping device to rise, the rollers 94allow the head 30 to move with respect to the arm 44 in the direction ofmovement of the conveyor chain without this relative movementintroducing any effort opposing the movement of the chain because thecontact between the rollers 94 and the head 30 is rolling and notsliding.

As can be seen, the mechanism according to the invention allows thegripping device of each mechanism to be controlled quickly, withconsiderable force, and without introducing parasitic effort on theconveyor chain.

What is claimed is:
 1. A temperature condition oven for a blow-moldingfacility for producing containers of thermoplastic material, comprising:a conveyor chain of links having gripping devices each of which isintended to carry a blank of the container to move it around a circuitinside the oven, with the chain being driven in continuous movementalong its circuit, wherein each gripping device is axially movable withrespect to the link that carries it so that when it is taken from anextreme release position to an extreme gripping position it engagesaxially on the neck of the blank, the oven further comprising means forcontrolling the movements of the gripping devices between their releaseand gripping positions, wherein the means for controlling the movementsof the gripping devices comprises at least one mechanism provided withan arm that is movable along a trajectory that is essentially parallelto the axial direction of gripping and which carries an interface devicethat comes into contact with the gripping device, with the interfacedevice movably mounted on the arm in such a way as to allow non-slipcontact with the gripping device while being immobilized with respect tothe arm along the axial direction of gripping.
 2. The oven according toclaim 1, wherein the arm is controlled in its trajectory along amovement that alternates between an initial position and a finalposition and, for a position of contact of the arm that falls betweenits initial and final positions, the interface device comes into contactwith the gripping device which is in one of its extreme positions andforces it towards the other of its extreme positions, which positioncorresponds to the final position of the arm.
 3. The oven according toclaim 1, wherein the interface device is mounted on the arm so that itis movable in a direction parallel to the movement of the links of thechain.
 4. The oven according to claim 3, wherein the interface device iselastically drawn back to a rest position with respect to the arm, andas a result of the movement of the corresponding chain link between themoment the arm comes into contact with the interface device and themoment the arm reaches its final position, the interface device is movedaway from its rest position by the gripping device with which it is incontact.
 5. The oven according to claim 4, wherein between the contactposition and the final position of the arm, the gripping devicecooperates by adherence to the interface device to move it away from itsrest position with respect to the arm.
 6. The oven according to claim 4,wherein, during the return movement of the arm from its final positionto its initial position, the interface device is drawn back to its restposition by elastic means.
 7. The oven according to claim 3, wherein theinterface device is mounted on the arm slideably in the direction ofmovement of the links of the chain.
 8. The oven according to claim 1,wherein the interface device is comprised of at least one roller whichis mounted on the arm rotatably around an axis perpendicular to theaxial direction of gripping and to the direction of the movement of thelinks of the chain.
 9. The oven according to claim 8, wherein, betweenthe moment the interface device comes into contact with the grippingdevice and the moment the arm reaches its final position, the grippingdevice cooperates by adherence to the interface device to drive theroller in rotation around its axis.
 10. The oven according to claim 1,wherein the gripping device has a rod one central section of which isaxially guided in the corresponding link and the two opposite ends ofwhich cooperate respectively with the blank and with the mechanism,wherein the mechanism exerts a pushing force on the rod, and furtherwherein the interface device cooperates by pressing against one surfaceof the rod that is essentially flat and perpendicular to the axialdirection.
 11. The oven according to claim 3, wherein the grippingdevice has a rod one central section of which is axially guided in thecorresponding link and the two opposite ends of which cooperaterespectively with the blank and with the mechanism, wherein themechanism exerts a pulling force on the rod, wherein the interfacedevice has the shape of a U-section having two parallel limbs the endsof which are turned inward to delimit an aperture allowing the rod topass through, and further wherein the rod of the gripping devices has acontrol head which is intended to move between the two limbs of theU-section and which has a width that is greater than the width of theaperture in such a way that when the interface device is moved axiallyby the arm, the turned ends of the U-section cooperate with the head tocontrol the axial movement of the gripping device.
 12. The ovenaccording to claim 8, wherein the gripping device has a rod one centralsection of which is axially guided in the corresponding link and the twoopposite ends of which cooperate respectively with the blank and withthe mechanism, wherein the mechanism exerts a pulling force on the rod,wherein the arm has the shape of a U-section having two parallel limbsthe ends of which are turned inward to delimit an aperture allowing thepassage of the rod, wherein each of the two turned ends has at least oneroller (94), and further wherein the rod of the gripping devices carriesa control head that is intended to move between the two limbs of theU-section and which has a width that is greater than the width of theaperture in such a way that when the arm is moved axially, the rollersof the turned ends of the U-section cooperate with the head to controlthe axial movement of the gripping device.
 13. The oven according toclaim 1, wherein the alternating movement of the arm is controlled by aconnecting rod and crank system.
 14. The oven according to claim 1,wherein the means for controlling the movements of the gripping meanscomprise two mechanisms, one of which controls the movement of thegripping devices from their extreme release position to their extremegrip position, and the other controls the reverse movement.